IPSEC VPN - Unable to get traffic working - non-standard setup

[jimmyjamesjimmy]

Hello,

I'm relatively new to PFSense firewalls. I've configured an IPSEC VPN between a Sophos XG115 and PFSense. The tunnel is up, but I can't seem to get traffic going through, not even ping.

I figure it could be my unusual setup.
Site1: is the XG115 side.
Site2: is the PFSense side. It's setup is a bit different. First up is the Internet modem which has clients plugged into the network ports. One of the clients is a PC with 1x NIC running PFSense.

I can ping the lan devices from the PFSense diagnostics. But I figure because PFSense is not the main router on the network or the primary WAN device, it doesn't know how to send the VPN traffic to the lan devices connected to the switch built into internet modem?

Does anyone know how I can pass traffic from the VPN to the lan devices connected to the modem? Do I need to create some routes or firewall rules?

Kind regards
Jimmy